It is known to provide bearings such as ball bearings or roller bearings with temperature sensors. For monitoring the bearing, heat generated at the interface of balls/rollers and the raceways is detected by a temperature sensor located as close as possible to this interface. This makes a cage of a bearing a desirable position for temperature measurement. However, a bearing cage is rotating and cannot be easily accessed and the available space is narrow. In particular for smaller bearings, it is difficult to integrate batteries or a generator into the bearing cage.
The document EP 1 849 013 B1 discloses a bearing having a cage equipped with a power receiving coil. A transmitter for sending a signal indicative of the sensed condition of the bearing to further antennae arranged on the outer race is integrated in the cage. However, this solution is feasible only for larger bearings with a cage capable of supporting the transmitter electronics.
Passive wireless temperature sensors for bearing cages have been proposed e.g. in the article “A Passive Wireless Temperature Sensor for Harsh Environment Applications”, Sensors 2008, 7982-7995 by Ya Wang, Yi Jia, Qiushui Chen and Yanyun Wang. A passive oscillator circuit including a temperature dependent capacitance and an inductor is arranged on a cage such that the inductor coil interacts with a transmitter coil of a driven oscillator circuit arranged on a non-rotating ring of the bearing. The temperature dependence of the capacitance results in a temperature dependence of the resonance frequency of the resonant circuit in the cage which can be measured. Similar systems have been investigated by S. Scott et al of the Purdue University, see e.g. http://docs.lib.purdue.edu/nanopub/1089.
The resonant circuit in the cage absorbs energy from the primary circuit with a coil on the non-rotating ring such that the resonant frequency can be derived from an absorption peak in the frequency sweep. The method measures the energy missing at the oscillation frequency.
It is further known to equip train bearing units or train axleboxes of high-speed trains with polyamide cages. These train bearing units are sometimes monitored using hot-box infrared scanners arranged alongside the track. These infrared scanners detect increased temperature in bearing components to detect defective bearings. While the polyamide cages have turned out to be safer than the formerly used steel cages, the defects in polyamide cages will not be detectable using the hot-box infrared scanners. The detection of cage failure would also be useful in aerospace bearings, high-speed bearings and may other applications.
The invention seeks to provide improved polymer cages for bearings with simplified possibility to detect cage damage.